The field of the invention is coating processes using electrical or radiant energy, wherein synthetic resin is contained in the coating. The present invention is particularly concerned with a process for producing covering, opaque films and coatings from coating compositions containing light curable synthetic resins.
The use of light curable synthetic resins, necessitated by the presence of unsaturated groups, in coating compositions for producing coatings is already known. Solutions of unsaturated polyester in copolymerizable monomers are used as coating compositions for wood, metal and other substrates.
It is known that the light curing synthetic resins is effected by irradiation of UV light. In principle, photochemically effective sensitizers which permit polymerization of the unsaturated portions of the synthetic resin are used in this process. The UV hardening process can only be used if the coating composition contains no substances which prevent the passage of the rays. In practice, this means that only transparent coating compositions can be cured by means of UV rays. Thus, transparent coatings are obtained from transparent coating agents using the light curing process.
If it is wished to obtain covering, opaque coatings, the coating composition must contain covering pigments or dyes. The UV hardening process cannot be used in these cases.
The term "coating compositions" in this text refers to all liquid forms of preparations which are necessary for producing coatings, films and lacquer components such as pore filler, coating lacquer, primer, filler, etc.
The term "coatings" in the present text refers to all layers, coatings, lacquers or films, obtained from the above-mentioned coating compositions.
The term "light curable" as used in the text refers to coating compositions which can be cured by irradiation with UV light, sunlight or powerful ionizing rays.
The term "light curing" refers to the process of curing using UV light, sunlight or powerful ionizing radiation.
Irradiation curing processes, according to the state of the art, are summarized, for example, in "The Light Hardening of Polyester Lacquers" (Die Lichthartung von Polyesterlacken) Eugen Richter, Moderne Holzverarbeitung (Modern Wood Processing), Vol. 10, (1968), pages 604 - 606 and "Lackhartung durch ultraviolettes Licht" (Lacquer Hardening by Ultraviolet Light), Dr. W. Deninger and Dr. M. Partheiger, Undustrie-Lackjer-Betrieb, 37 Jg. V.3, March 1969, pages 85 - 91.
The state of the art of photopolymerizable compositions may be ascertained by reference to U.S. Pat. Nos. 3,196,098 of Walter Edwing Mochel, 3,008,242 of Sites et al, 3,013,895 of Agruss, 3,060,023 of Burg et al, 3,511,687 of Keyl et al, and 3,551,311 of Nass et al, and Belgian Pat. No. 714,605, the disclosures of which are incorporated herein.
U.S. Pat. No. 3,511,687 discloses the state of the art of curing of polyester resin coatings by radiant energy. The resins used in the patent are disclosed in U.S. Pat. Nos. 3,006,878 and 2,852,487.